This proposal outlines the development and implementation of a multicellular recording method to study encoding of information by olfactory sensory neurons. Sensory information about odor is extracted by many different olfactory neurons simultaneously and distributed as trains of action potentials to glomeruli throughout the olfactory bulbs. The response of an olfactory sensory neuron to odor is usually described as excitatory, but in studies of isolated neurons, both excitatory and inhibitory odor responses have been reported, and the same odor can alter different membrane conductances in different neurons. The presence of such variability has raised questions about whether the responses are real or artifactual, and it has emphasized how limited our knowledge of the fundamental nature of the encoding process is. Present methods are not well suited for critically examining odor encoding. We propose to develop a new multicellular electrical recording technique to address the problem This technique will permit recording of odor- elicited electrical activity at the single-cell level simultaneously from a small population of olfactory sensory neurons. Such a capability would represent a technological breakthrough that could significantly advance our understanding of olfactory neural encoding. The method will utilize isolated olfactory epithelial tissue together with an array of independent glass microelectrodes, each recording extracellular action currents from the exposed cilia of olfactory sensory neurons. The neurons would remain in the intact tissue and not require degradative enzymatic treatment, thus allowing odor responses to be recorded under nearly physiological conditions. Because of its multicellular nature coupled with the possibility of long-term recordings, the method offers a unique, high-throughput physiological assay of odor responses. It should be ideal for studying the fundamental mechanisms of odor encoding with pharmacological tools, and it will offer an efficient means to study transgenic animals which are expensive to engineer.